Lets do some experimentation, to see how we could get/interpret the length of different dict/array values in a dict.
create our test dict, see list and dict comprehensions:
>>> my_dict = {x:[i for i in range(x)] for x in range(4)}
>>> my_dict
{0: [], 1: [0], 2: [0, 1], 3: [0, 1, 2]}
Get the length of the value of a specific key:
>>> my_dict[3]
[0, 1, 2]
>>> len(my_dict[3])
3
Get a dict of the lengths of the values of each key:
>>> key_to_value_lengths = {k:len(v) for k, v in my_dict.items()}
{0: 0, 1: 1, 2: 2, 3: 3}
>>> key_to_value_lengths[2]
2
Get the sum of the lengths of all values in the dict:
>>> [len(x) for x in my_dict.values()]
[0, 1, 2, 3]
>>> sum([len(x) for x in my_dict.values()])
6